rimental improvements of all kinds are very likely to be outweighed at first by their inconveniencies, whatever may be the skill and caution of the persons concerned in them; and it is natural that an ignorant or prejudiced observer should be at least as strongly impressed by the instances of failure as by those of success, and should be encouraged by the supposed accuracy of his own observations on the progress of others, to persevere in inveterate errors of various kinds, which more candour and more humility might possibly have enabled him to correct. The enlightened author of the present work has very truly observed, that the frequent failure of experiments, conducted after the most refined theoretical views, 'is far from proving the inutility of such trials; one happy result, which can generally improve the methods of cultivation, is worth the labour of a whole life; and an unsuccessful experiment, well observed, must establish some truth, or tend to remove some prejudice.'

On the other hand, it has been frequently remarked, that the public of Great Britain not immediately connected with the landed interest, has felt no other effect from the magnificent scale, on which the modern improvements of agriculture have been conducted, than the limitation of the supply of the table by an extravagant enhancement of the price of provisions, the curtailment of the enjoyment of rustic scenery by the progress of enclosure, the depression of gentlemen and noblemen into swineherds, and the elevation of a new order of uneducated beings into comparative opulence.

But that partial evils may have arisen from widely extended improvements, is no proof that the benefits on the whole have not preponderated. If our population has increased, it is of urgent necessity that a greater supply of food should be procured for its consumption; and if the improvements in agriculture have rendered it possible to obtain a greater quantity of food independently of foreign supply, it is natural and just that the farmers concerned in raising it should be enriched! if enriched, they must be less dependent on the immediate demand of a purchaser, and the prices must be somewhat advanced; unless indeed the apparent increase of prices is to be attributed to the depreciation of the value of the circulating medium, which is by no means an impossible supposition. We do not profess any very high respect for the intellectual dignity of the mechanical and servile pursuits inseparable from the occupation of the mere agriculturist, however they may be combined with superiority of talents and elegance of manners; but it is happy for many that such a combi nation is practicable; that without any degradation of their rank and consideration, the idle may find some amusing employment.

and the less opulent some source of additional income, in devoting a portion of their time and attention to the original occupations of the heroes and patriarchs of remote antiquity.

Should the public have been disposed to form its expectations of the excellence of this work, from the unexampled success which has attended the former labours of the author in philosophical chymistry, it is probable that some disappointment may have been felt by many of its readers. We have however no right to demand from an individual that he should be uniformly fortunate; although we are persuaded that such a philosopher as Sir Humphry Davy can on no occasion be otherwise than respectable. In the experimental pursuit of general chymistry, an investigator is at liberty to follow those paths of inquiry which offer him the fairest prospects; but where his object is precisely limited to a given point of immediate utility, it is not in the power of human intellect to command a certainty of striking improvement. If however a sufficient store of information is furnished, to give employment to a thinking mind, and to enable it to pursue its own researches, without tempting it to advance rashly upon principles merely speculative, the end of such a publication is in a great measure answered: and so much as this, and more, the present work appears very successfully to have effected.

Of the eight lectures which it contains, the first is a general introduction to the subject; the second an outline of the principles of physical science, especially as affecting vegetables; the third is devoted to the structure of plants, and the chymical properties of the substances which they contain; the fourth relates to soils and their analysis; the fifth to the atmosphere, and to the functions of vegetation; the two next to vegetable and mineral manures, and the last to the effects of burning and irrigation, and to the economy of crops. An appendix contains the results of an elaborate series of experiments on the nutritive matter afforded by grasses, performed at Woburn by order of the Duke of Bedford.

The first and second lectures, however well adapted for the information of the audience to whom they were addressed, and of the readers for whom they are intended, cannot be expected to contain much of novelty or of scientific interest. In the third the doctrine of the circulation of the sap is stated, according to the theory and experiments of Hales, Grew, Darwin, Mirbel, and especially of Mr. Knight. The ascent of the sap through the alburnum, its modification by the action of the air, and by other circumstances to which it is exposed in the leaves, and its descent through the bark, are considered as preparatory to the formation of the 'cambium,' a mucilaginous fluid found between the bark and the alburnum, which is supposed to be a mixture of the

ascending and descending sap, affording, by a sort of precipitation, a concrete substance, which constitutes the new wood and bark. Sir H. Davy infers from the late observations of Mr. Palisot de Beauvois, as a partial exception to this theory, that the sap may be transferred to the bark, so as to exert its nutritive functions independent of any general system of circulation :-in the case of the maple and the lilac, small annual shoots were produced in the parts where the bark was insulated:' at the same time the growth of the bark in such cases appears to have been extremely limited. The author is disposed to adopt Mr. Knight's conjecture respecting the use of the silver grain, or radiating fibres of the wood, in propelling the sap, by its alternate expansions and contractions, depending on the daily changes of temperature: but we cannot say that we think any thing is gained by this conjecture. It has not been shown, or even rendered probable, that the silver grain has any powers of expansion materially different from those of the other parts of the vegetable ; and no attempt has been made to enable us to imagine in what manner this alternate expansion and contraction, if it actually took place, could operate at all upon the sap, much less how its magnitude could by any means be adequate to the production of such a force as would be required. In short, we must be contented, for the present, with confessing our total ignorance of the means by which the sap is propelled, being only assured that every theory, which has yet been advanced to explain it, is without foundation. As, however, the roots must attract moisture, and absorb it into their pores, with a certain force, whether of a mechanical, chymical, electrical, or vital nature, it is not impossible that the new substance, thus attracted, may simply urge onwards the former contents of the vessels, as a condition indispensable to its introduction; and it appears to us that this conjecture, if it does not afford much of a satisfactory explanation, is at least liable to no positive objection. The evaporation from the leaves must also tend to co-operate in promoting the ascent of the sap where the natural connexion is preserved, since it must produce a capillary suction so much the more powerful, as the tubes concerned are smaller, and consequently capable of drawing up the sap to a height almost unlimited; but not of forcing it upwards in the manner that the sap of vegetables is forced up in experiments similar to those of Dr. Hales. The remainder of the lecture is principally chymical: we shall only extract the result of one process lately discovered.

Mr. Cruikshank, by exposing syrup to a substance named phosphuret of lime, which has a great tendency to decompose water, converted a part of the sugar into a matter analogous to mucilage: and Mr. Kirchof, recently, has converted starch into sugar by a very simple

process, that of boiling in very diluted sulphuric acid. The proportions are 100 parts of starch, 400 parts of water, and 1 part of sulphuric acid by weight. The mixture is to be kept boiling for forty hours; the loss of water by evaporation, being supplied by new quantities. The acid is to be neutralized by lime, and the sugar crystallized by cooling. This experiment has been tried with success by many persons. Dr. Tuthill, from a pound and a half of potato starch, procured a pound and a quarter of crystalline brown sugar; which he conceives possessed properties intermediate between cane sugar and grape sugar. The acid is decomposed, and-no elastic matter is set free.p. 128.

We must also make a short extract from the very interesting table of the quantities of nutritive matter afforded by different substances.-P. 150.

In the analysis of such substances, the gluten is separated by kneading or rubbing them with water, so as to form it into a coherent mass; the starch is deposited by the water thus employed; the remaining solution, when heated, often affords flakes of albumen; the extract mixed with the sugar may be separated from it either by crystallizing the sugar, first dissolved in alcohol, or by boiling the mixture long, in contact with the air, which will render the extract insoluble.

The most important part of the fourth lecture is that which relates to the analysis of soils, and we shall endeavour to reduce the author's directions on this subject into a form somewhat more concise.

1. The soil, previously well dried, is to be heated for 10 or 12 minutes over an Argand's lamp, in a temperature of 300°, which may be ascertained by keeping a bit of wood in contact with the bottom of the dish, and taking care that it be not charred. If the loss of weight is only from 2 to 5 per cent. the soil is but slightly absorbent, and probably siliceous: when the soil is very retentive of water, the loss may amount to as much as 12 per cent. and such soils are generally either aluminous, or rich in vegetable or animal matter.

2. Vegetable fibres and gravel are to be separated by sifting, and their weights noted: whether the fragment may be calcarious, effervescing with acids, or siliceous, scratching glass, or aluminous, capable of being cut with a knife, and not effervescing.

3. The finer parts, thus separated, being boiled in 3 or 4 times their weight of water, the coarsest sand will fall to the bottom in a minute, the finer in 2 or 3: the parts still remaining suspended may be collected on a filter, while the water is preserved for further examination. 4. The sand may be examined as the gravel has already been: the portion dissolved by muriatic acid being chiefly calcarious, the remainder siliceous.

5. For analyzing the finer parts, they must be exposed to the action of at least twice their weight of muriatic acid, diluted with twice as much water, for an hour or two, being occasionally stirred. The triple prussiate of potass and iron must be added as long as it throws down a blue precipitate, which, when ignited, will leave pure oxyd of iron, sometimes mixed with a little manganese. [We must not however forget to deduct the iron of the triple prussiate.] The solution must then be made alkaline by the neutral carbonate of potass, which will precipitate the carbonate of lime: and by boiling it for a quarter of an hour the carbonate of magnesia will also be thrown down. Any alumina accidently taken up will be found with the lime, and may be separated by boiling the earth for a few minutes in a little soaplees, or solution of caustic soda, which dissolves alumina. Sometimes a sufficient estimate of the carbonate of lime present may be formed from the loss of weight during solution in an acid, the gas expelled constituting 43 per cent. of the whole carbonate.

6. The parts undissolved by the acid are to be strongly ignited in a crucible, with the addition of a little nitrate of ammonia if expedition be required: the loss of weight indicating the quantity of animal and vegetable matter present.

7. The remaining parts will be principally alumina and silica, with oxyd of iron and manganese, these are to be boiled for 2 or 3 hours with a little more than their weight of sulphuric acid, diluted with 4 times as much water, which will dissolve the alumina and the oxyds. The succinate of ammonia will throw down the oxyd of iron, and soaplees will dissolve the alumina, leaving the manganese behindY

VOL. XI. NO. XXII.